The discussion revolves around interpretations of the Aharonov-Bohm effect, particularly focusing on the nature of the gauge potential and its ontological status. Participants explore the implications of considering the gauge potential as an ontic entity, the relationship between gauge potentials and measurable quantities, and the conceptual distinctions between different fields in electromagnetism.
Participants express differing views on the ontological status of the gauge potential and its relationship to measurable quantities. There is no consensus on whether the gauge potential should be considered an ontic entity or how it relates to the electric field.
The discussion includes various assumptions about the nature of fields and their representations, as well as the implications of gauge invariance on observability. Some participants reference specific theories and literature to support their claims, but these references do not resolve the ongoing debate.
Physics can never answer all possible questions. Any physical theory will eventually "bottom out" in statements that cannot be analyzed further.JandeWandelaar said:Can physics ever tell?
I think though that an interpretation that offers a mechanism for chance is to be preferred. I find "empty" chance hard to imagine.PeterDonis said:No interpretation can "solve" anything since all QM interpretations make the same experimental predictions, and in any case, as I said, we currently can't experimentally test whether macroscopic objects exhibit quantum effects or not. Interpretations of QM at this point are just forms of speculation or personal opinions about how our future knowledge might develop--but none of those developments have happened yet.
I think a non-pointlike structure of gravitons eliminates singularities. How can a black hole singularity (or divergence of integrals) form if particles are non-pointlike? (Just an aside, I know its not mainstream, but strings are not point-like either).vanhees71 said:Fine, but it should be clear that all physical theories are complete as long as there is no reproducible phenomenon that proves them wrong. Then you need to refine the theory or even find a completely new one. The old theory then doesn't become completely obsolete but you learn about the constraints of their applicability. There's no constraint yet known concerning quantum theory.
It's also clear that there's still no satisfactory quantum theory of the gravitational interaction. In this sense QT is also incomplete, but as far as particle physics is concerned, quantum gravity effects are very hard to observe, so that at least FAPP concerning particles QT is complete.
Is it the B-field inside the solenoid that induces the phaseshift of the electron field? Isn't a gauge on the electron field performed?PeterDonis said:Not everywhere. If you have a region of space where there is no magnetic field anywhere (for example, a double slit experiment with no solenoid placed between the slits), there will be no Aharonov-Bohm effect.
Which is your personal opinion. Maybe some day we'll be able to test such things. But we can't now, so it all comes down to people's opinions. There's no way to settle such questions unless and until we can do so by experiment.JandeWandelaar said:I think though that an interpretation that offers a mechanism for chance is to be preferred.
What do you think? If the B field inside the solenoid is not there, there is no effect. If the B field inside the solenoid is there, there is an effect. What does that tell you?JandeWandelaar said:Is it the B-field inside the solenoid that induces the phaseshift of the electron field?
How would you do such a thing? What does "performing a gauge on the electron field" mean experimentally? Experimentally, the thing that makes the difference is whether the solenoid with its B field is there or not.JandeWandelaar said:Isn't a gauge on the electron field performed?
There is a B-field in the thin solenoid only. But no B-field outside it. An example of non-locality?PeterDonis said:What do you think? If the B field inside the solenoid is not there, there is no effect. If the B field inside the solenoid is there, there is an effect. What does that tell you?How would you do such a thing? What does "performing a gauge on the electron field" mean experimentally? Experimentally, the thing that makes the difference is whether the solenoid with its B field is there or not.
Possibly. Some physicists seem to think so.JandeWandelaar said:There is a B-field in the thin solenoid only. But no B-field outside it. An example of non-locality?
How would you tell? You can't measure the phase of the electron directly.JandeWandelaar said:Isn't the phase of the electron field changed globally on both sides of the solenoid?
Yes.JandeWandelaar said:If you reverse the current, the pattern shifts to the opposite side.
Again, what would this mean experimentally? How would you experimentally "perform a gauge on the field"? If that is just another word for "putting a solenoid in" or "reversing the current", why not just say plainly what you're doing in the experiment?JandeWandelaar said:Isn't a gauge performed on the field?
Isn't the shifted pattern proof of the phase changes of the electron field on both sides of the solenoid?PeterDonis said:Again, what would this mean experimentally?
Why would it be, since you can't measure the phase change?JandeWandelaar said:Isn't the shifted pattern proof of the phase changes of the electron field on both sides of the solenoid?
But isn't the pattern a measurement of the phase change?PeterDonis said:Why would it be, since you can't measure the phase change?
Of course in a particular theoretical model the shifted pattern indicates a phase change, but that's in the theoretical model. The model is not reality.
It's a measurement of relative phase, but not absolute phase. Perhaps that is where we have a disconnect. You can't measure absolute phase, but yes, you can measure relative phase with things like interference patterns.JandeWandelaar said:But isn't the pattern a measurement of the phase change?
So it is like potential energy? Only differences that count?PeterDonis said:It's a measurement of relative phase, but not absolute phase. Perhaps that is where we have a disconnect. You can't measure absolute phase, but yes, you can measure relative phase with things like interference patterns.
As far as measurements go, yes.JandeWandelaar said:So it is like potential energy? Only differences that count?
Which means the A-field is a real thing?PeterDonis said:As far as measurements go, yes.
I thought the interesting part of the Bohm-Aharonov was the vanishingly small overlap of the B field producing very large changes in measured particle flux. Not an absolute phase change.PeterDonis said:You can't measure absolute phase, but yes, you can measure relative phase with things like interference patterns.
But both with and without the solenoid you measure relative phases. The solenoid induces a global phase change on both sides of it.PeterDonis said:It's a measurement of relative phase, but not absolute phase. Perhaps that is where we have a disconnect. You can't measure absolute phase, but yes, you can measure relative phase with things like interference patterns.
The A-field is not the same thing as relative phase, so I don't see why a measurement of relative phase would indicate that the A-field "is a real thing".JandeWandelaar said:Which means the A-field is a real thing?
Yes, and the relative phase change is different in the two cases.JandeWandelaar said:both with and without the solenoid you measure relative phases.
What does "global phase change" mean? If it's just another way of saying "the relative phase changes with the solenoid present", why not just say the latter?JandeWandelaar said:The solenoid induces a global phase change on both sides of it.
In the subthread you responded to, we are talking about the effect in a double slit experiment, where the observable is the interference pattern at the detector. The pattern changes when a solenoid is present. The pattern is basically a measurement of relative phase (beween the "paths" coming from the two slits).hutchphd said:I thought the interesting part of the Bohm-Aharonov was the vanishingly small overlap of the B field producing very large changes in measured particle flux.
But it makes the same measurable predictions as standard QM. Or do you think that it doesn't?martinbn said:I think that BM is a different theory.
Yes I know that. As usual with these discussions I have lost track of what the damned question on the table is. And everyone is answering a slightly different question vociferously (using QM written in dogma speak). No mas.PeterDonis said:In the subthread you responded to, we are talking about the effect in a double slit experiment, where the observable is the interference pattern at the detector. The pattern changes when a solenoid is present. The pattern is basically a measurement of relative phase (beween the "paths" coming from the two slits).
I means that the phase of the electron wave is changed non-arbitrarily over the whole region between the double slit and the screen. Not everywhere the same, which would have no effect, but neither locally, which would have caused photons.PeterDonis said:What does "global phase change" mean? If it's just another way of saying "the relative phase changes with the solenoid present", why not just say the latter?
But we aren't measuring everywhere. We're only measuring relative phase at the detector screen, and observing how it changes when we add a solenoid. So how do we know what the phase is everywhere?JandeWandelaar said:I means that the phase of the electron wave is changed non-arbitrarily over the whole region between the double slit and the screen.
I don't understand this. Why would changing the phase "locally" "cause photons"?JandeWandelaar said:Not everywhere the same, which would have no effect, but neither locally, which would have caused photons.
What the is a particle according to classical physics? A localized mass or charge with a momentum? Which leaves the question what charge is. If you consider mass an interaction effect, there is a connection between mass and charge. If charge is defined as the coupling to the associated gauge field (say electric charge and the photon field), then maybe the wavefunction is a means to let the particle "explore" space (within the confines of that wavefunction) to be able to interact with other particles. Still, what charge IS will still be a mystery. Maybe a "longing" to interact, but now I truly stray into a weird domain...PeterDonis said:Depends on the theory. QM doesn't, but classical physics did. That's why some people think QM is an incomplete theory.
Isn't the A-field caused by local gauge transformations, i.e., interaction by means of photons which "make up" for the gauge changes?PeterDonis said:I don't understand this. Why would changing the phase "locally" "cause photons"?
The A-field can be changed in the math by local gauge transformations, but most physicists view that as solely a mathematical convenience, not corresponding to anything physical.JandeWandelaar said:Isn't the A-field caused by local gauge transformations, i.e., interaction by means of photons which "make up" for the gauge changes?
I think this question is basically the same as asking if virtual particles are real. There is an interaction between the solenoid and the electron field between the slits and the screen. You can see this as mediated by virtual photons. Are they real? The pattern shift is real for sure. But if virtual photons are not, how then can they influence the pattern?PeterDonis said:The A-field can be changed in the math by local gauge transformations, but most physicists view that as solely a mathematical convenience, not corresponding to anything physical.
It might help if you gave a reference for where you are getting the understanding you describe here.
We have multiple Insights articles on this (and plenty of previous threads); this one is probably the best one to start with:JandeWandelaar said:I think this question is basically the same as asking if virtual particles are real.
This is circular reasoning: you're assuming a particular model in which virtual particles are real and cause the pattern, and then you're trying to argue that because the pattern is real, the virtual particles must be real.JandeWandelaar said:The pattern shift is real for sure. But if virtual photons are not, how then can they influence the pattern?
I have had a lot of discussions about virtual particles. And they are involved here too. The standard, so I have experienced, is to consider them mathematical aid. I think you can consider them real. It can be considered an opinion though. It's my opinion that they are real, the opinion of others that they are not. You can leave them out in bootstrap or S-matrix approaches, but they still have effect. You can't observe them obviously, and what means a particle with zero energy and non-zero momentum? So it's simple. One considers them truly present in the vacuum, and others don't. Òne thing's sure. They are not exchanged, nor popping up as pairs.PeterDonis said:We have multiple Insights articles on this (and plenty of previous threads); this one is probably the best one to start with:
https://www.physicsforums.com/insights/misconceptions-virtual-particles/This is circular reasoning: you're assuming a particular model in which virtual particles are real and cause the pattern, and then you're trying to argue that because the pattern is real, the virtual particles must be real.
It's always a mistake to confuse models with reality. Virtual particles are part of one particular model--and even that is less than it appears, since that model is based on perturbation theory, which can't even be used to make predictions about many phenomena (and one of them, AFAIK, is in fact the Aharonov-Bohm effect). The fact that a certain observable phenomenon is real can never, by itself, prove that every entity in a particular theoretical model about that phenomenon is real.